2,6-Difluoro­benzoic acid

In the title compound, C₇H₄F₂O₂, the dihedral angle between the benzene ring and the carboxyl­ate group is 33.70 (14)°. In the crystal structure, inversion dimers linked by pairs of O—H...O hydro­gren bonds occur, generating R₂²(8) loops. The dimers are linked into sheets lying parallel to (102) by C—H...F hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.049
• wR factor = 0.143
• Data-to-parameter ratio = 18.9

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          7
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600         30

Alert level G
PLAT063_ALERT_4_G Crystal Size Likely too Large for Beam Size ....       0.73 mm
PLAT720_ALERT_4_G Number of Unusual/Non-Standard Labels ..........          1

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   2 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The derivatives of 2,6-diflorobenzylchloride involved in the inhibition of phosphodiesterases (PDEs) are enzymes which catalyze PDEs. These derivatives are classified into seven families, five of which, PDE1–PDE5, have been characterized (Beavo, 1995). The hydrolysis of cyclic nucleotides was evaluated according to the methods in given the references (Beavo & Reifsnyder, 1990; Nicholson et al., 1991).

The molecule of the title compound, (I), (Fig. 1) is not planar with the dihedral angle between the benzene ring and the carboxylate group being 33.70 (14)°. In the crystal structure, the molecules are linked into pairs of centrosymmetric dimers by intermolecular O2—H1O2···O3 hydrogren bonds (Table 1). These dimers are linked into two-dimensional plane by the intermolecular C3—H3A···F2 hydrogen bonds (Fig. 2, Table 1) parallel to (102).

Related literature

For general background to 2,6-diflorobenzylchloride derivatives, see: Beavo (1995); Beavo & Reifsnyder (1990); Nicholson et al. (1991). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986).

S2. Experimental

2,6-Difluorobenzylchloride (0.01 mol, 1.7 g) was added drop-wise with stirring into a round bottom flask containing 25 ml water and then refluxed for two and half hours. The gum compound precipitate formed was filtered and dissolved in alkaline water. Hydrochloric acid was then added drop-wise with stirring. The white precipitate formed was dissolved in methanol. Colourless needles of (I) were formed at room temperature overnight and filtrated and dried at 333 K.

S3. Refinement

All hydrogen atoms were located in a difference Fourier map and refined freely.

Computing details

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of (I) with 50% probability ellipsoids for non-H atoms.
	Fig. 2. The crystal packing of (I), viewed down the b axis, showing two 2-D planes.

2,6-Difluorobenzoic acid

Crystal data

C7H4F2O2	F(000) = 320
Mr = 158.10	Dx = 1.666 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3166 reflections
a = 3.6517 (4) Å	θ = 3.3–32.1°
b = 14.1214 (15) Å	µ = 0.16 mm^−1
c = 12.2850 (13) Å	T = 100 K
β = 95.651 (3)°	Needle, colourless
V = 630.42 (12) Å^3	0.73 × 0.19 × 0.09 mm
Z = 4

Data collection

Bruker APEXII DUO CCD diffractometer	2190 independent reflections
Radiation source: fine-focus sealed tube	1895 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
φ and ω scans	θmax = 32.1°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −5→5
Tmin = 0.841, Tmax = 0.986	k = −20→20
6112 measured reflections	l = −18→18

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.049	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.143	All H-atom parameters refined
S = 1.12	w = 1/[σ^2(Fo^2) + (0.0668P)^2 + 0.3079P] where P = (Fo^2 + 2Fc^2)/3
2190 reflections	(Δ/σ)max < 0.001
116 parameters	Δρmax = 0.47 e Å^−3
0 restraints	Δρmin = −0.31 e Å^−3

Special details

Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
F1	0.0410 (3)	−0.01635 (6)	0.16839 (7)	0.0312 (2)
F2	0.2348 (3)	0.26707 (6)	0.36896 (7)	0.0285 (2)
O2	0.2287 (3)	0.09843 (7)	0.46658 (7)	0.0238 (2)
O3	0.4751 (3)	−0.00746 (7)	0.35958 (8)	0.0222 (2)
C1	0.0163 (4)	0.07830 (9)	0.17659 (9)	0.0194 (2)
C2	−0.1413 (4)	0.12763 (10)	0.08679 (10)	0.0228 (3)
C3	−0.1734 (4)	0.22519 (10)	0.09441 (10)	0.0234 (3)
C4	−0.0482 (4)	0.27250 (10)	0.19005 (11)	0.0230 (3)
C5	0.1044 (4)	0.22003 (9)	0.27793 (9)	0.0184 (2)
C6	0.1398 (3)	0.12160 (8)	0.27576 (9)	0.0160 (2)
C7	0.2939 (3)	0.06665 (8)	0.37288 (9)	0.0156 (2)
H2	−0.221 (7)	0.0927 (16)	0.0182 (18)	0.038 (6)*
H3	−0.285 (6)	0.2599 (15)	0.0302 (17)	0.035 (5)*
H4	−0.074 (6)	0.3406 (16)	0.1979 (18)	0.035 (5)*
H1O2	0.341 (11)	0.062 (3)	0.526 (3)	0.098 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
F1	0.0518 (6)	0.0183 (4)	0.0219 (4)	0.0019 (4)	−0.0044 (4)	−0.0039 (3)
F2	0.0459 (6)	0.0169 (4)	0.0210 (4)	−0.0010 (4)	−0.0048 (4)	−0.0018 (3)
O2	0.0340 (6)	0.0238 (5)	0.0135 (4)	0.0038 (4)	0.0014 (4)	0.0013 (3)
O3	0.0269 (5)	0.0179 (4)	0.0216 (4)	0.0056 (4)	0.0012 (4)	0.0030 (3)
C1	0.0238 (6)	0.0181 (5)	0.0162 (5)	0.0001 (4)	0.0014 (4)	0.0003 (4)
C2	0.0242 (6)	0.0289 (6)	0.0150 (5)	−0.0002 (5)	−0.0006 (4)	0.0019 (4)
C3	0.0224 (6)	0.0289 (6)	0.0184 (5)	0.0037 (5)	−0.0001 (4)	0.0078 (4)
C4	0.0272 (6)	0.0193 (6)	0.0225 (6)	0.0041 (5)	0.0016 (5)	0.0062 (4)
C5	0.0210 (5)	0.0174 (5)	0.0166 (5)	0.0004 (4)	0.0012 (4)	0.0011 (4)
C6	0.0182 (5)	0.0160 (5)	0.0137 (4)	0.0009 (4)	0.0014 (4)	0.0019 (3)
C7	0.0174 (5)	0.0148 (5)	0.0148 (4)	−0.0006 (4)	0.0020 (4)	0.0012 (3)

Geometric parameters (Å, º)

F1—C1	1.3442 (15)	C2—H2	0.99 (2)
F2—C5	1.3467 (14)	C3—C4	1.3892 (19)
O2—C7	1.2794 (14)	C3—H3	0.98 (2)
O2—H1O2	0.96 (4)	C4—C5	1.3807 (17)
O3—C7	1.2574 (15)	C4—H4	0.97 (2)
C1—C2	1.3815 (17)	C5—C6	1.3965 (17)
C1—C6	1.3976 (16)	C6—C7	1.4866 (15)
C2—C3	1.387 (2)
C7—O2—H1O2	113 (2)	C5—C4—H4	119.3 (13)
F1—C1—C2	117.86 (11)	C3—C4—H4	122.2 (13)
F1—C1—C6	118.83 (11)	F2—C5—C4	117.84 (11)
C2—C1—C6	123.29 (12)	F2—C5—C6	118.74 (10)
C1—C2—C3	118.58 (12)	C4—C5—C6	123.38 (11)
C1—C2—H2	119.4 (13)	C5—C6—C1	115.44 (10)
C3—C2—H2	122.0 (13)	C5—C6—C7	122.18 (10)
C2—C3—C4	120.79 (11)	C1—C6—C7	122.37 (11)
C2—C3—H3	118.2 (13)	O3—C7—O2	123.76 (11)
C4—C3—H3	121.0 (13)	O3—C7—C6	119.51 (10)
C5—C4—C3	118.49 (12)	O2—C7—C6	116.72 (10)
F1—C1—C2—C3	179.13 (13)	C4—C5—C6—C7	−177.92 (12)
C6—C1—C2—C3	1.2 (2)	F1—C1—C6—C5	−179.87 (12)
C1—C2—C3—C4	0.3 (2)	C2—C1—C6—C5	−1.92 (19)
C2—C3—C4—C5	−0.9 (2)	F1—C1—C6—C7	−0.65 (19)
C3—C4—C5—F2	178.01 (12)	C2—C1—C6—C7	177.31 (12)
C3—C4—C5—C6	0.0 (2)	C5—C6—C7—O3	−147.25 (13)
F2—C5—C6—C1	−176.65 (11)	C1—C6—C7—O3	33.57 (18)
C4—C5—C6—C1	1.31 (19)	C5—C6—C7—O2	33.33 (17)
F2—C5—C6—C7	4.12 (18)	C1—C6—C7—O2	−145.84 (13)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1O2···O3^i	0.95 (4)	1.68 (4)	2.6318 (14)	174 (4)
C3—H3···F2^ii	0.98 (2)	2.54 (2)	3.3428 (16)	138.7 (16)

Symmetry codes: (i) −x+1, −y, −z+1; (ii) x−1, −y+1/2, z−1/2.